The invention relates to a method and a circuit for the commutation of brushless direct-current motors (BLDC motors), without using sensors, and especially to a method and a circuit for producing rotor position signals, without using sensors, for the commutation of brushless DC motors.
Whereas in brushed DC motors, magnet coils are disposed in the rotor and at least one permanent magnet is disposed in the stator, the brushless direct-current motor is distinguished primarily in that the magnet coils lie in the stator and the rotor is provided with one or more permanent magnets. In this arrangement, no abrading contacts to the power supply or commutation of magnet coils is necessary, so as to preclude disadvantages connected with that, in particular the known brush sparking, which can cause significant high-frequency disturbances (EMI [electromagnetic interference]), as well as wear on the brushes and collectors.
Brushless direct-current motors have, therefore, a significantly higher reliability and service life, as well as greater efficiency and diminished running noise. Moreover, they cause no soiling due to abrasion or burn by the contact brushes. These motors are realizable as both internal-rotor and external-rotor motors, whereby internal-rotor motors especially have the additional advantage of better heat dissipation from the magnetic coils in comparison to brushed DC motors.
Brushless direct-current motors (BLDC motors) are realized as endurance runners in the most diverse performance ranges.
To operate a BLDC motor, the magnetic coils must be controlled on a delayed basis with currents of predetermined direction, so that the magnetic field built in the stator turns and entrains the rotor. Toward this end, i.e., in order to achieve a chronologically correct commutation of the coil currents, information is needed regarding the current place or position of the rotor relative to the magnetic coils.
A difference needs to be made here between recording the rotor position with and without sensors and the corresponding commutation of the coil currents or motor control, which is carried out by it.
A sensor-supported recording of the rotor position can, for example, take place by means of magnetic sensors (for example, Hall effect sensors, field plates), electrical sensors (potentiometers, for example) or optical sensors (for example, encoders or resolvers), while during a detection without sensors, the mutually-induced voltage (back EMF) of the rotor in an uncontrolled magnet coil is captured and analyzed.
Both ways of determining rotor position include disadvantages.
While in sensor-supported capture, the above-named sensors can be seen as disadvantageous on the basis of their additional costs as well as the amount of space needed, in detection without sensors, the problem often arises that the mutually-induced voltage captured is overlaid with inductive disturbing pulses, if a current is still flowing through the coils up to the time of the electrical separation of the coils in question. The extent of these disturbing pulses basically depends on the mechanical load on the motor shaft. Because these disturbing pulses can reach very great amplitudes and a not insignificant duration, they are not disposed of adequately with analog filtering by and large, so that they are also overlaid to the reconstructed position or commutation signals and don't provide a reliable commutation of the coils under all motor conditions.
In motors with coils connected in a star circuit as in FIG. 1A, there is furthermore the problem that the star point N needed to measure the voltage induced by the rotor in one of the coils is not usually taken-out of the motor separately, so that it must be reconstructed electrically.
Even though there are several advantages to this, such a reconstruction in general, it is relatively costly or relatively inexact, especially if the motor is to be operated under very different load conditions.
It is desirable to provide a cost-efficient, space-saving and reliable option, with which brushless direct-current motors can be electrically commutated.
It is also desirable to specify a process and a circuit for the production of rotor position signals for the commutation of brushless direct-current motors without using sensors, with which a simple, reliable, and in particular disturbance-free commutation is possible, even under unfavorable load conditions.
According to an aspect of the present invention, a process is provided for the production of rotor position signals for the commutation of brushless direct-current motors without using sensors via the following steps:
production of emulated (i.e., reproduced) Hall sensor signals through differentiation of the voltages adjoining the motor's coil terminals which are not supplied with current, which voltages are mutually-induced by a rotor of the motor in the coils; and
production of rotor position signals by stopping the emulated Hall sensor signals for a period after the appearance of an edge change of these signals, which minimally corresponds to the time period or the interval of the disturbing pulses from this edge change which overlay the emulated Hall sensor signals.
According to another aspect of the present invention, a circuit is provided for production of rotor position signals without using sensors to commutate brushless direct-current motors, which has a first device for production of emulated Hall sensor signals, by differentiating voltages adjoining coil terminals of the direct-current motor, which are not supplied with current, which are mutually-induced by a rotor in the coils, as well as a second device for suppression of disturbing pulses in the Hall sensor signals, and in particular according to a process according to one of claims 1 to 3.
A particular advantage of this solution consists in that the additional circuit complexity is relatively light and cost-effective, and for example can be realized as part of a broader integrated motor control unit.